In ink jet printers, of both the drop on demand and continuous kinds, there is a basic conflict between two attributes desired for the printing inks. On the one hand, it is very desirable that the ink on a printed output sheet not be smearable, e.g., when fed to an output tray or pick-up for handling. This mitigates toward quick-dry ink characteristics. On the other hand, the ink jet printer will have conditions of non-use, e.g. over-nights, and it is desirable that the inks used for printing do not clog the fluid system, e.g. by drying in critical locations such as the printing orifices.
Various solutions have been devised to reduce the "smear or clog" problems. Ink has been modified to absorb more rapidly into the sheet; however, this can cause spreading and reduced print sharpness. Special ink-fixing paper can be utilized; however, this increases material costs and can detract from the output sheet characteristics. Special storage and start-up procedures can be utilized to avoid ink clogging in the printer; however, this adds to printer cost and complexity.
Another approach has been to heat the print sheet and/or ink image to dry the ink more quickly. Radiant energy lamp sources have been provided on the output sheet path for this purpose, but must be controlled carefully not to darken or burn the print sheet. Rollers with embedded heat sources have been used to transfer heat by conduction to the back of a print sheet. This contact heating approach is desirable; however, it too has had drawbacks. Either a separate sheet heating roller must be provided along the sheet feed path, or a roller portion of the normal sheet support and transport system must be heated. Separate heating rollers add cost and require space. The incorporation of a heater into operative sheet transport system components has involved replacement of the entire sheet feed component, when the heater fails.